Fuel injection nozzles for gas turbine engines, for safety reasons, must be made so as to eliminate any possibility of fuel leakage where housing or body parts are joined together. In addition, it is desirable that such parts have a threaded connection for clamping other nozzle parts therebetween. Such threaded and welded parts are well known in the fuel injection nozzle art. In many cases it is desirable to be able to disassemble the parts in order to clean or repair the nozzle and then reassemble and reweld the threaded parts. In such cases the weld joint should be designed so that it can be cut through by a tool and then rewelded. This poses a special problem because when the weld is cut through there may be formed a radially inwardly projecting burr on the internally threaded part which will pass over the external thread when the parts are unthreaded from each other. If the burr projects inwardly to or below the diameter of the external thread there is considerable risk that the burr will damage the thread upon separation of the parts.
One method of preventing thread damage in such nozzle parts is disclosed in Mains U.S. Pat. No. 3,709,529 wherein the diameter of the weld joint is substantially larger than the major diameter of the threads so that any radially inwardly projecting burr that is formed by cutting of the weld joint will still be large enough to pass over the external thread without damaging the same.
Another method of preventing damage to a thread upon separation of the nozzle parts after cutting through the weld joint is disclosed in Clemenshaw et al (U.S. Pat. No. 3,024,045). This patent discloses a ring of refractory material, such as carbon, between the end faces of the two threaded together parts. The weld metal is exterior of the refractory ring and the latter prevents formation of radially inward burrs to a diameter less than the diameter of the external thread when the joint is cut to thereby prevent damage to the external thread when the parts are separated.
The methods described in the above mentioned patents are satisfactory from a functional standpoint. However, space and cost limitations in some instances make it desirable that some other method or construction be used.